The present invention relates to distortion-free, opposite-phase current sources which can be used in electronic variable controlled amplifiers, electronic controllers or the like.
Heretofore, an opposite-phase current source has been known such as shown in FIG. 1, in which transistors Q.sub.1, Q.sub.2, Q.sub.3 and Q.sub.4 are provided with the same characteristics, and resistors R.sub.1, R.sub.2, R.sub.3 and R.sub.4 connected to emitters of the respective transistors have the same resistance value. The transistors Q.sub.1 and Q.sub.4 form an opposite-phase current source, which is connected to an electronic tone controller 1. The bases of the transistor Q.sub.1 and Q.sub.2 are connected to each other so as to form two current mirror circuits. The parallel-connected transistors Q.sub.2 and Q.sub.3 are connected in series to a constant current source 2 so as to operate as a subtraction circuit. The bases of the transistors Q3 and Q4 are connected to each other so as to form two current mirror circuits, which act as a source of current. The amount of current flowing from the constant current source 2 is determined so as to be twice as large as the collector current of the transistor Q.sub.1 at the time when no input signal is applied. Accordingly, when no input signal is being received, equal collector currents flow in the four transitors Q.sub.1 through Q.sub.4.
When an a.c. signal is applied to an input terminal 3, the signal thus applied is translated into a current with the aid of the transistor Q.sub.1. The current flowing in the transistor Q.sub.1 in turn flows through the transistor Q.sub.2. The current flow from the constant current source 2 is subtracted from by the current flowing through the transistor Q.sub.2, and an opposite-phase current flows through the transistor Q.sub.3. The same amount of current flowing through the transistor Q.sub.3 also flows through the transistor Q.sub.4. Consequently, oppositephase currents are obtained from the transistor Q.sub.1 and Q.sub.4.
In the circuit arranged as described above, there is a disadvantage in that due to distortions or noise produced by the two current mirror circuits, the opposite-phase current taken out from the transistor Q.sub.4 is distorted.